1. Field of the Invention
The present invention relates to a loudspeaker, particularly but not exclusively a loudspeaker configured to reproduce high frequency audio signals (e.g., a tweeter for use in a multi-way loudspeaker system).
2. State of the Art
Loudspeaker systems comprising open-backed drive units which radiate sound in both a forward and rearward direction are well known in the art. Such drive units may comprise a voice coil coupled to the rear of a diaphragm and a magnet assembly for interacting with the voice coil to move the diaphragm. The magnet assembly may have an aperture for allowing sound radiated from the rear of the diaphragm to pass through the magnet assembly.
Sound waves radiated from the rear of an open-backed drive unit may be out of phase with those emitted from the front of the drive unit. Accordingly, care must be taken to take account of interference between sound radiated in a rearward direction (hereinafter “rearward radiation”) and sound radiated in a forward direction (hereinafter “forward radiation”). One common solution is to house the rear of each drive unit in an enclosure or baffle (e.g., cabinet) in order to isolate or in some way modify the rearward radiation to prevent undesirable interference. However, the presence of an enclosure at the rear of a drive unit will generally result in a mismatch in the acoustic impedance presented to the front and the rear of the drive unit. Unless the enclosure is carefully designed, this mismatch can have a highly detrimental effect on sound quality.
Various arrangements have been proposed in the art to minimize the detrimental effects of the mismatch in forward and rearward acoustic impedance. For example, open-backed drive units for use as tweeters have been developed where the magnet assembly comprises a short tubular enclosure for receiving rearward radiating sound. However, such an enclosure will generally have a large resonant peak at a frequency related to the dimensions of the tube.